In an OFDM (orthogonal frequency division multiplexing) system, the PAPR (peak-to-average power ratio) is high. Because a signal having a high PAPR tends to cause distortion in a power amplifier, numerous methods have been proposed to reduce the PAPR. One of the proposed methods is PTS (partial transmit sequence), which has a feature of being able to reduce the PAPR without causing signal distortion, making it a preferable method for use in actual systems. PTS is a method whereby a plurality of subcarriers in an OFDM system are divided into a number of groups, and phase rotations are performed to the subcarrier signals for each group so as to reduce the PAPR. The groups into which the plurality of subcarriers is divided are called segments.
A receiver must acquire the phase rotations that are performed to the subcarrier signals included in each segment in the transmitter. As a method of the transmitter notifying the receiver of the phase rotations, for example, the transmitter transmits a reference symbol having a known phase in each segment, and the receiver estimates the phase rotation of each segment performed by PTS from the displacement of the phase of the reference symbol.
In the above-described method, because a subcarrier into which a reference symbol is inserted cannot transfer data, the data rate drops. Because a reference symbol is necessary for each segment, the data rate drops in proportion to the number of segments. If there are a large number of subcarriers in the OFDM system, the degree of data rate reduction is very small. However, if the amount of information in the reference symbols is increased in order to achieve robustness in the notification of the phase rotation performed by the PTS, the effect of data rate reduction by the reference symbols might increase.